The present invention relates to a mechanism for rotating and driving a mirror body of an electrically powered foldable outer rearview mirror for a motor vehicle, especially to a rotating and driving mechanism for the mirror body having an improved stability and reliability.
An outer rearview mirror for a motor vehicle is known to be mounted protruding from the vehicle side and can be designed to be foldable so as not to stand in the way of parking the vehicle in a garage or the like.
A foldable outer rearview mirror system disclosed in Published Japanese Patent Application Hei 2-290754 comprises a shaft, a mirror housing rotatably supported on the shaft and a clutch means controlling the rotation of the mirror housing. The shaft includes a bottom flange portion, a cylindrical portion provided protruding from the flange portion and a pair of arc-shaped grooves provided on the flange portion at the opposite sides of the cylindrical portion.
While a bracket is provided at the bottom of the mirror housing, the surface where the mirror body is rotated and supported and a pair of semi-spherical recesses are provided on the undersurface of the bracket. Balls are retained in the semi-spherical recesses and are engaged with the arc-shaped grooves provided on the fixed surface of the flange to rotate the mirror housing around the shaft. The mirror housing is rotated by driving force means including motor and a gear means or the like. The arc-shaped groove has a predetermined step in it to determine the movement of balls.
In the system described hereinbefore, when the motor is operated to rotate the mirror housing to the backward position, the balls approach one step of the arc-shaped grooves and the motor is electrically cut off just before the balls contact with the steps. Then the driving force transmission means has gears or the like which have back-lash so as not to halt the rotation of the mirror housing simultaneously with the stop of the motor operation. The mirror housing is rotated by inertia until the balls contact with the steps.
The mirror housing is rotated to the normal position and the motor is electrically cut off just before the balls contact with the other steps of the arc-shaped grooves to rotate the mirror housing by inertia so that balls contact with the steps to halt the rotation of the mirror housing.
When the rearview mirror contacts with the stop means, balls are rotated on the fixed surface extending between the steps to locate the mirror housing at the forward position.
Instead of disconnecting the electric power supply to the motor just before balls approach to the steps, a method of connecting PTC (Positive Thermal Coefficient) element with the electric power supply line of the motor to control the motor operation is also disclosed in Published Japanese Utility Model Registration Application No. Hei 4-76196.
The PTC element has a characteristic that the resistance rapidly increases to a certain temperature range of the line so that the temperature rise of the electric power supply line is detected when balls contact with the steps to control the operation of the motor.
In a conventional system for an automatically foldable rearview mirror system:
1. the backward position and the normal position of the mirror housing are stopped by contacting a pair of balls with the steps in the arc-shaped grooves; it is difficult to achieve an even contact condition of balls with the steps even though the motor operation is stopped and the back-lash of the driving force transmission means is set aside all together, and chattering occurs at the mirror housing position;
2. the arc-shaped groove is formed on the fixed surface and permits water and foreign substance such as a dust or the like to easily become lodged therein so that balls cannot slide smoothly to stop the rotation of the mirror housing and further the stop position of the mirror housing is changed and
3. the temperature of the electric power supply line is detected by PTC element to control the motor operation so that the motor is still supplied with electric power during the increase of the temperature for a long time which is caused by the motor load; the mirror housing is inclined on the fixed surface when balls start to pass over the steps.